Field of the Invention
The present invention relates to a robot calibrating apparatus and a robot calibrating method in a robot apparatus that includes a multi-jointed arm driven through control on multiple joints and utilizes a visual sensor, and a robot apparatus and a method of controlling a robot apparatus.
Description of the Related Art
Conventionally, a robot apparatus has become widespread which includes a vertical multi-jointed arm, an end effector (hereinafter, called a robot body) and a controlling apparatus for controlling these elements, and further includes a visual sensor (hereinafter, also called a camera) attached to a tip end part of the arm. In this robot apparatus, an object, such as a workpiece, is measured through the camera, and the controlling apparatus operates the position and orientation of the object from a measurement result and controls the position and orientation of the robot body based on the position and orientation of the object acquired through the operation.
In general, a measurement coordinate system adopted by the camera as a reference is different from an operation coordinate system adopted by the robot body as a reference. Accordingly, to acquire an operation target value (command value) of the robot body from a measurement value of the camera, the measurement value of the camera in the measurement coordinate system is required to be transformed into the value in the operation coordinate system. For this coordinate transformation, it is required to perform a preliminary calibrating operation between the measurement coordinate system and the operation coordinate system and acquire a calibration value (a coordinate transformation expression).
As an example of the calibrating operation, for instance, a method has been known that is called a hand-eye calibration method. This method sequentially moves a robot body to multiple positions and orientations, and causes a camera to measure a reference object for calibration at each position and orientation (see Japanese Patent Application Laid-Open No. H10-063317, and Radu Horaud and Fadi Dornaika, “Hand-Eye Calibration”, International Journal of Robotics Research Vol. 14, No. 3, 195-210, 1995). This method acquires the relationship between the operation coordinate system and the measurement coordinate system, based on the relationship between a command value for the tip end part of the robot body at each position and orientation of this robot body and a measurement value of a reference object for calibration from the camera, so as to minimize a residual, and then acquires a calibration value.
The coordinate calibrating method described in Japanese Patent Application Laid-Open No. H10-063317 does not consider an operational error of a robot body. In actuality, an operational error occurs owing to mechanical error or bending at an arm. There are further errors that are other than operational error and are specific to a robot body; these errors include an assembly error and lens distortions. These errors cannot be sufficiently suppressed by conventional coordinate calibrating methods, and prevent accuracy from being improved in control of the position and orientation of the robot body.